1. Field of the Invention
The present invention relates to an electron-emitting device, an electron source and an image-forming apparatus using it, and production methods thereof.
2. Related Background Art
The conventionally known electron-emitting devices are roughly classified under two types as a thermionic cathode and as a cold-cathode. The cold-cathode emission sources include field emission type (hereinafter referred to as xe2x80x9cFE typexe2x80x9d) devices, metal/insulator/metal type (hereinafter referred to as xe2x80x9cMIM typexe2x80x9d) devices, surface conduction electron-emitting devices, and so on.
Examples of the FE type devices known include those disclosed in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) or in C. A. Spindt, xe2x80x9cPhysical Properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976), and so on.
Examples of the MIM type devices known include those disclosed in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Appl. Phys., 32, 646 (1961), and so on.
Examples of the surface conduction electron-emitting devices include those disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965), and so on.
The surface conduction electron-emitting devices utilize such a phenomenon that electron emission occurs when electric current is allowed to flow in parallel to the surface in a thin film of a small area formed on a substrate. Examples of the surface conduction electron-emitting devices reported heretofore include those using a thin film of SnO2 by Elinson cited above, those using a thin film of Au [G. Ditmmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)], those using a thin film of In2O3/SnO2 [M. Hartwell and C. G. Fonsted: xe2x80x9cIEEE Trans. ED Conf.,xe2x80x9d 519, (1975)], those using a thin film of carbon [Hisashi Araki et al.: Shinku (Vacuum), Vol. 26, No. 1, p22 (1983)], and so on.
A typical device configuration of these surface conduction electron-emitting devices is the device structure of M. Hartwell cited above, which is shown in FIG. 18. In the same drawing, numeral 1 designates an electrically insulative substrate. Numeral 4 denotes an electrically conductive, thin film, which is, for example, a thin film of a metallic oxide formed in an H-shaped pattern by sputtering and in which an electron-emitting region 5 is formed by energization operation called forming described hereinafter. In the drawing the gap L between the device electrodes is set to 0.5-1 mm and the width Wxe2x80x2 to 0.1 mm.
In these conventional surface conduction electron-emitting devices, it was common practice to preliminarily subject the conductive film 4 to the energization operation called forming, prior to execution of electron emission, thereby forming the electron-emitting region 5. Namely, the forming is an operation for applying a dc voltage or a very slowly increasing voltage, for example at the increasing rate of about 1 V/min, to the both ends of the conductive film 4 to locally break, deform, or deteriorate the conductive film, thereby forming the electron-emitting region 5 in an electrically high resistant state. In the electron-emitting region 5 a fissure is formed in part of the conductive film 4 and electrons are emitted from near the fissure. The surface conduction electron-emitting device experiencing the aforementioned forming operation is arranged so that electrons are emitted from the above-stated electron-emitting region 5 when the current flows in the device with application of the voltage to the above-described conductive film 4.
On the other hand, in the case of another surface conduction electron-emitting device, for example, as disclosed in Japanese Laid-open Patent Application No. 7-235255, the device having experienced the forming is sometimes subject to a treatment called an activation operation. The activation operation is a step by which significant change appears in the device current If and in the emission current Ie.
The activation step can be performed by repetitively applying pulse voltage to the device, as in the case of the forming operation, under an ambience containing an organic substance. This operation causes carbon or a carbon compound from the organic substance existing in the ambience to be deposited at least on the electron-emitting region of the device, so as to achieve outstanding change in the device current If and in the emission current Ie, thereby achieving better electron emission characteristics.
An image-forming apparatus can be constructed by using an electron source substrate having a plurality of such electron-emitting devices as described above and combining it with an image-forming member comprised of a fluorescent member and other members.
The image-forming apparatus including the displays etc., however, has been and is required to have higher performance according to quick steps to multimedia society with recent increase in sophistication of information. Namely, requirements are increase in the size of screen, decrease in power, increase in definition, enhancement of quality, decrease in space, etc. of the display devices.
With the aforementioned electron-emitting devices, there is thus a desire for the technology for keeping stable electron emission characteristics in still higher efficiency and for longer time so as to permit the image-forming apparatus employing the electron-emitting devices to provide bright display images on a stable basis.
The efficiency herein means a current ratio of electric current emitted into vacuum (hereinafter referred to as emission current Ie) to electric current flowing (hereinafter referred to as device current If), when the voltage is applied between a pair of opposed device electrodes of the surface conduction electron-emitting device.
It is, therefore, desirable that the device current If be as small as possible and that the emission current Ie be as large as possible.
If the highly efficient electron emission characteristics can be stably controlled over long time, we will be able to realize a bright and high-definition image-forming apparatus of low power, for example a flat television, in the case of the image-forming apparatus, for example, using the fluorescent member as an image-forming member.
It is, however, the present status of the aforementioned M. Hartwell electron-emitting device that the device is not always satisfactory yet as to the stable electron emission characteristics and the electron emission efficiency and that it is very difficult to provide a high-luminance image-forming apparatus with excellent operation stability using it.
It is necessary for use in such application that sufficient emission current Ie be obtained by a practical voltage (for example, 10 V-20 V), that the emission current Ie and device current If not vary largely during driving, and that the emission current Ie and device current If not be degraded over long periods of use. The conventional surface conduction electron-emitting device of M. Hartwell had the following problem, however.
As shown in FIG. 18, the surface conduction electron-emitting device of M. Hartwell has the electron-emitting region 5 nearly perpendicular to the direction of application of voltage.
An object of the present invention is to provide an electron-emitting device having good electron emission characteristics and an electron source using it and to provide a high-luminance image-forming apparatus using the electron-emitting devices.
Another object of the present invention is to provide an electron-emitting device demonstrating minimized change in the electron-emitting characteristics and an electron source using it and to provide an image-forming apparatus capable of maintaining high luminance over a longer period, using the electron-emitting devices.
The present invention provides an electron-emitting device comprising, on a substrate, a pair of electrodes, an electroconductive film having a gap in part, connected to said pair of electrodes, a member comprising a principal component of carbon, provided in the gap portion while being connected to the electroconductive film, and a metallic oxide comprising at least one element selected from the group consisting of nickel, iron, and cobalt, between said member comprising the principal component of carbon and said substrate.
The present invention also provides an electron-emitting device comprising, on a substrate, a pair of electrodes, an electroconductive film having a gap in part, connected to said pair of electrodes, and a member comprising carbon having an orientation of a layer structure substantially parallel to a surface of the substrate, said member being provided in the gap portion while being connected to the electroconductive film.
The present invention provides an electron source for emitting electrons according to an input signal, wherein a plurality of the electron-emitting devices as set forth are arrayed on a substrate.
The present invention also provides an image-forming apparatus for forming an image, based on an input signal, said image-forming apparatus comprising an image-forming member and the electron source as set forth.
The present invention provides a production method of electron-emitting device comprising a step of forming an electroconductive film on a film comprising a metallic oxide comprising at least one element selected from the group consisting of nickel, iron, and cobalt, provided between a pair of electrodes on a substrate, a step of forming a gap in part of the electroconductive film, and a step of forming a member comprising a principal component of carbon in a connected state to the electroconductive film, in the gap portion.